Very long optical fiber transmission paths, such as those employed in undersea or transcontinental terrestrial lightwave transmission systems which employ optical amplifier repeaters, are subject to decreased performance due to a host of impairments that accumulate along the length of the optical fiber comprising the transmission path. Typically, these impairments vary with time and cause a random fluctuation in the signal-to-noise ratio of the received signal. These impairments can arise from accumulated noise effects caused, for example, by polarization hole-burning ("PHB") in the erbium-doped fiber used in the optical amplifiers and waveform distortions caused by chromatic dispersion and optical nonlinearities throughout the transmission path. Scrambling the state-of-polarization of the launched optical signal to depolarize the optical carrier can improve the received signal-to-noise by reducing PHB. In my co-pending U.S. patent application Ser. No. 08/312,848, an arrangement is disclosed where the polarization scrambling frequency is chosen as the clock frequency that defines the bit rate of the transmitter. Such a technique may provide for more efficient use of optical bandwidth in wavelength division multiplexed ("WDM") systems. This bit-synchronous polarization scrambling is also a particularly advantageous trade-off between the two regimes of low-speed and high-speed scrambling. In addition to the synchronous polarization scrambling, superimposed phase modulation ("PM") can dramatically increase the eye opening of the received data pattern. The increase in eye opening results from the conversion of PM into bit-synchronous amplitude modulation ("AM") through chromatic dispersion and nonlinear effects in the fiber.